In the formula given in the Definition, what is the point of including the y'' /= y' condition, given that y'' >- y'? Could a solution ever Pareto-dominate itse

In the formula given in the Definition, what is the point of including the y'' /= y' condition, given that y'' >- y'? Could a solution ever Pareto-dominate itself? If we know that A dominates B, do we not know that they are distinct?